Power converters

ABSTRACT

A power converter capable of improving converter&#39;s efficiency and achieving zero-voltage-switching is provided, in which a first series circuit is connected in parallel with a direct current (DC) power supply and has a first inductor, a first primary winding, first and second switching elements connected in series. A second series circuit is connected in parallel with the DC power supply and has third and fourth switching elements, a first capacitor, a second primary winding and a second inductor connected in series. A second capacitor is connected between a first node between the first primary winding and the first switching element in the first series circuit and a second node between the fourth switching element and the second primary winding in the second series circuit. A third node between the first and second switching elements is connected to a fourth node within the second series circuit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to power converters, and more particularly, topower inverters capable of achieving zero-voltage-switching (ZVS) toimprove converter's efficiency and reducing input current ripple toalleviate the electromagnetic interference intensity (EMI).

2. Description of the Related Art

To reduce the size and weight with faster dynamic response, PWM powerconverters are operated at high frequencies. However, there are severalinherent problems, such as the increase of the switching losses and theparasitic oscillation noise. Thus, the operating frequency of PWMconverters is limited. To alleviate these problems, soft-switchingtechniques, zero-voltage-switching (ZVS) and/or zero-current switching,are widely used to minimize the switching losses. Employing phase shiftmodulation or asymmetrical pulse width modulation scheme, several highfrequency zero-voltage full-bridge topologies for high powerapplications were disclosed.

For example, U.S. Pat. No. 6,466,458, issued to Zhang et al, disclosesan asymmetrical full bridge DC-to-DC converter with a linear controlcharacteristic of output voltage to switching duty cycle and an optimalreset of the transformer core.

U.S. Pat. No. 5,198,969, issued to Redl et al, discloses a phase-shiftedfull bridge DC-to-DC converter capable of reducing switching losses oftransistors and rectifier diodes.

Further, U.S. Pat. No. 4,864,479, U.S. Pat. No. 5,946,200 and U.S. Pat.No. 6,504,739 all disclose full bridge DC-to-DC converters capable ofreducing switching losses. However, the above mentioned soft switchingfull-bridge converters have a larger pulsating input current rippleinherent problem. In addition to the dv/dt phenomenon, the pulsatinginput current ripples, di/dt, causes the power converters having EMIproblems. The lower the pulsating current ripples, the lower the EMIintensity to be dealt with. Consequently, a smaller EMI filter can beused to meet the EMI regulations. Moreover, a lower RMS value of theinput current can be also achieved resulting in improving the converterefficiency. Therefore, low input current ripple power converter hasadditional advantage and becomes one of the design criteria of concern.

Thus, there is a need for a high frequency soft switching powerconverter with a lower input current ripple and high conversionefficiency.

BRIEF SUMMARY OF THE INVENTION

The invention provides an embodiment of a power converter consisting oftwo series-connected circuitries, connected in parallel with the DCpower supply, and one clamp capacitor. The first series circuitcomprises a first inductor, a first primary winding, a first switchingelement and a second switching element connected in series. The secondseries circuit comprises a third switching element, a first capacitor, afourth switching element, a second primary winding and a second inductorconnected in series. The clamp capacitor is connected between a firstnode within the first series circuit and a second node within the secondseries circuit. The first node is between the first primary winding andthe first switching element, the second node is between the fourthswitching element and the second primary winding, and a third nodebetween the first and second switching elements is connected to a fourthnode within the second series circuit.

The invention provides another embodiment of a power converterconsisting of two series-connected circuits, connected in parallel withthe series-connected DC power supply and first inductor, and two clampcapacitors. The first series circuit, comprises a second inductor, afirst primary winding, a first switching element, a second switchingelement, a second primary winding and a third inductor connected inseries. The second series circuit comprises a fourth inductor, a thirdprimary winding, a third switching element, a first capacitor, a fourthswitching element, a fourth primary winding and a fifth inductorconnected in series. The first clamp capacitor is connected between afirst node within the first series circuit and a second node within thesecond series circuit, in which the first node is between the firstprimary winding and the first switching element, and the second node isbetween the fourth switching element and the fourth primary winding. Thesecond clamp capacitor is connected between a third node within thefirst series circuit and a fourth node within the second series circuit,in which the third node is between the second switching element and thesecond primary winding, the fourth node is between the third primarywinding and the third switching element, and a fifth node between thefirst and second switching elements is connected to a sixth node withinthe second series circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be more fully understood by reading the subsequentdetailed description and examples with references made to theaccompanying drawings, wherein:

FIG. 1 shows an embodiment of a power converter according to theinvention;

FIG. 2 shows an equivalent diagram of the switching elements shown inFIG. 1;

FIG. 3 shows the gate driver signal's waveforms of the power converteroperated in an asymmetrical mode;

FIGS. 4A˜4D show operation diagrams of the power converter operated inthe asymmetrical mode;

FIG. 5 shows the gate driver signal's waveforms of the power converterwhen operated in a phase shift mode;

FIG. 6 shows another embodiment of the power converter according to theinvention;

FIG. 7 shows another embodiment of the power converter according to theinvention;

FIG. 8 shows another embodiment of the power converter according to theinvention;

FIG. 9 shows another embodiment of the power converter according to theinvention;

FIG. 10 shows another embodiment of the power converter according to theinvention and

FIGS. 11A˜11D show the possible rectifier circuits applied to theembodiments according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The following description is of the best-contemplated mode of carryingout the invention. This description is made for the purpose ofillustrating the general principles of the invention and should not betaken in a limiting sense. The scope of the invention is best determinedby reference to the appended claims.

FIG. 1 shows an embodiment of a power converter according to theinvention. As shown, a power converter 100A comprises a transformer T1,switching elements SW1˜SW4, capacitors C1 and C2, and inductors L1 andL2. The transformer T1 comprises two primary windings P1 and P2 and atleast one secondary winding S1, in which the inductor L1, the primarywinding P1 and the switching elements SW1 and SW2 are connected inseries to form a first series circuit, and the switching element SW3,the capacitor C1, the switching element SW4, the primary winding P2 andthe inductor L2 are connected in series to form a second series circuit.Both of the first and second series circuits are connected to a directcurrent (DC) power supply Vi in parallel. The inductors L1 and L2 can beparasitic inductors or external inductors.

The inductor L1 is connected between a first electrode (i.e., thepositive electrode) of the DC power supply Vi and the first terminal ofthe primary winding P1, and the primary winding P1 has a first terminalconnected to the inductor L1 and a second terminal connected to a nodeN1A. The switching element SW1 has a first terminal connected to thenode N1A and a second terminal connected to a node N3A, and theswitching element SW2 has a first terminal connected to the node N3A anda second terminal connected to a second electrode (i.e., the negativeelectrode) of the DC power supply Vi.

The switching element SW3 has a first terminal connected to the firstelectrode of the DC power supply Vi, and a second terminal connected toa node N4A, and the capacitor C1 has a first terminal connected to thenode N4A and a second terminal connected to the switching element SW4.The switching element SW4 has a first terminal connected to the secondterminal of the capacitor C1 and a second terminal connected to a nodeN2A. The primary winding P2 has a first terminal connected to the nodeN2A and a second terminal connected to the inductor L2, and the inductorL2 is connected between the second terminal of the primary winding P2,and the second electrode of the DC power supply Vi. In addition, thecapacitor C2 is connected between the nodes N1A and N2A, and the nodesN3A and N4A are connected together.

FIG. 2 shows an equivalent diagram of the switching elements shown inFIG. 1. As shown, a switching element SWX can be regarded as a switch, abody diode and a capacitor connected in parallel. In some embodiments,the switching elements SW1˜SW4 can also be implemented by bipolartransistors, IGBTs, or even electromechanical or micro-machinedswitches, with parallel-connected diodes. The switching elements SW1˜SW4are controlled by control signals provided by a converter controller,such as a phase shift modulation controller or a pulse widthasymmetrical modulation controller, thereby converting the DC powersupply Vi into an alternating current (AC) output at the secondarywinding S1. FIG. 3 shows the gate driver signal's waveforms of the powerconverter operated in an asymmetrical mode. For example, the voltageVgs1 is the gate driver signal of the switching element SW1, the voltageVgs2 is the gate driver signal of the switching element SW2, and so on.It should be noted that, when the switching elements SW1˜SW4 are turnedoff, the DC power supply Vi, the inductor L1, the primary winding P1,the capacitor C2, the primary winding P2, and the inductor L2 form aloop. Because polarity of the primaries P1 and P2 are opposite, theaverage voltage of the capacitor C2 can be equal to the DC supplyvoltage Vi. The operation waveforms will be described with reference toFIGS. 4A˜4D by following time intervals:

[t0,t1]

Referring to FIG. 4A, at time t0, the switching elements SW1 and SW2 areturned on under zero-voltage-switching condition and the switchingelements SW3 and SW4 are remained off. The DC power supply Vi, theinductor L1, the primary winding P1, the switching element SW1 and theswitching element SW2 form a first loop. The capacitor C2, the switchingelement SW1, the switching element SW2, the inductor L2 and the primarywinding P2 form a second loop. Both primary windings P1 and P2 areactivated, such that the magnetizing currents of the transformer T1increase linearly. In addition, the input ripple can be reduced becauseenergy delivered to the secondary winding S1 is provided by both of theDC power supply Vi and the average voltage of the capacitor C2. At thistime, the voltage stress cross the switching element SW3 is the DC powersupply Vi, and the voltage stress across the switching element SW4 isVi+VC1.

[t1,t2]

Referring to FIG. 4B, at time t1, the switching elements SW1 and SW2 areturned off. The voltage at the node N1A is increased, and magnetizingcurrents discharge the parasitic capacitors of the switching elementsSW3 and SW4. Finally, the parasitic capacitors of the switching elementsSW3 and SW4 are discharged completely and the body diodes of which areturned on.

[t2, t3]

Referring to FIG. 4C, at time t2, the switching elements SW3 and SW4 areturned on under zero-voltage-switching condition. The DC power supplyvoltage Vi, the switching element SW3, the capacitor C1, the switchingelement SW4, the primary winding P2 and the inductor L2 form a firstloop. The capacitor C2, the primary winding P1, the inductor L1, theswitching element SW3, the capacitor C1 and the switching element SW4form a second loop. The reset voltage −(Vi+VC1) is applied to theprimary windings P1 and P2, both primary windings are activated suchthat the magnetizing currents are decreased linearly and finallyreversed. Similarly, energy delivered to the secondary winding S1 isprovided by the DC power supply Vi and the average voltage of thecapacitor C2. At this time, the voltage stress across the switchingelement SW2 is the DC power supply Vi, and the voltage stress across theswitching element SW1 is Vi+VC1.

[t3, t4]

Referring to FIG. 4D, at time t3, the switching elements SW3 and SW4 areturned off. The voltage at the node N1A is decreased and magnetizingcurrents discharge the parasitic capacitors of the switching elementsSW1 and SW2. Finally, the parasitic capacitors of the switching elementsSW1 and SW2 are discharged completely and the body diodes of which areturned on. At time t4, the switching SW1 and SW2 are turned on to resumea new switching cycle.

In a steady operation, the relationship between the reset voltage andthe duty cycle can be expressed as:

${{Vi} + {{VC}\; 1}} = {\frac{D}{( {1 - D} )} \times {Vi}}$

For well understanding of operation of the power converter operated inan asymmetrical mode of the invention, operation features of this powerconverter are described as follows. First, the reset voltage ischangeable. With the decrease of the DC power supply Vi, the duty cycleincrease, and the reset voltage increases; the reset time shortens.Hence, the maximum duty cycle can be larger than 50% in low input, andthe conversion efficiency can be improved accordingly. Second, theswitching elements SW1˜SW4 are switched under zero-voltage-switching,and thus, the conversion efficiency can also improved. Third, voltagestresses of the switching elements SW2 and SW3 are equal to the DC powersupply Vi, and those of the switching elements SW1 and SW4 are equal tovoltage Vi+VC1. Thus, the power converter 100A is suitable forhigh-input voltage applications.

The power converter 100A can also be operated in a phase shift mode by aphase shift modulation controller. FIG. 5 shows the gate driver signal'swaveforms of the power converter when operated in a phase shift mode.Operations of the power converter 100A operated in the phase shift modeare similar to that operated in the asymmetrical mode, and thus areomitted for briefly.

FIG. 6 shows another embodiment of the power converter according to theinvention. As shown, the power converter 100B is similar to the powerconverter 100A, differing only, in that the node N3A is connected to thenode N4A″ between the capacitor C1 and the switching element SW4 ratherthan the node N4A between the capacitor C1 and the switching elementSW3. Operations of the power converter 100B are similar to those ofpower converter 100A, and thus are omitted for simplification.

FIG. 7 shows another embodiment of the power converter according to theinvention. As shown, a power converter 100C comprises a transformer T1,switching elements SW1˜SW4, capacitors C1˜C3, and inductors L1˜L5.

The transformer T1 comprises four primary windings P1˜P4 and at leastone secondary winding S1. The inductor L2, the primary winding P1, theswitching element SW1, the switching element SW2, the primary P2 and theinductor L3 are connected in series to form a first series circuit, andthe inductor L4, the primary winding P3, the switching element SW3, thecapacitor C1, the switching element SW4, the primary winding P4 andinductor L5 are connected in series to form a second series circuit. Theinductor L1 is connected between a first electrode (i.e. the positiveelectrode) of a direct current (DC) power supply Vi and the inductors L2and L4 in the first and second series circuits, and the inductor L1 isconnected to the DC power supply Vi in series. Both of the first andsecond series circuits are connected to the series-connected DC powersupply Vi and inductor L1 in parallel. The inductors L1˜L5 can beparasitic inductors or external inductors.

The inductor L2 is connected between the inductor L1 and the primarywinding P1. The primary winding P1 has a first terminal connected to theinductor L2 and a second terminal connected to a node N1B. The switchingelement SW1 has a first terminal connected to the node N1B, and a secondterminal connected to a node N5B, and the switching element SW2 has afirst terminal connected to the node N5B and a second terminal connectedto a node N3B. The primary winding P2 has a first terminal connected tothe node N3B and a second terminal connected to the inductor L3, and theinductor L3 is connected between the second terminal of the primarywinding P2 and a second electrode (i.e. the negative electrode) of theDC power supply Vi.

The inductor L4 is connected between the inductor L1 and the primarywinding P3, and the primary winding P3 has a first terminal connected tothe inductor L4 and a second terminal connected to a node N4B. Theswitching element SW3 has a first terminal connected to the node N4B,and a second terminal connected to a node N6B, and the capacitor C1 isconnected between the node N6B and the switching element SW4. Theswitching element SW4 has a first terminal connected to the capacitor C1and a second terminal connected to a node N2B, the primary winding P4has a first terminal connected to the node N2B and a second connected tothe inductor L5, and the inductor L5 is connected between the primarywinding P4 and the second electrode of the DC power supply Vi. Inaddition, the capacitor C2 is connected between the nodes N1B and N2B,and the capacitor C3 is connected between the nodes N3B and N4B, and thenodes N5B and N6B are connected together. The power converter 100C canalso be operated in the asymmetric mode with reference to FIG. 3. Itshould be noted that, when the switching elements S1 SW4 are turned off,the DC power supply Vi, the inductor L1, the inductor L2, the primarywinding P1, the capacitor C2, the primary winding P4, and the inductorL5 form a loop. The DC power supply Vi, the inductor L1, the inductorL4, the primary winding P3, the capacitor C3, the primary winding P2,and the inductor L3 form another loop. At this time, because polarity ofthe primaries P1 and P4 are opposite, the average voltage of thecapacitor C2 can be equal to the DC power supply Vi. Similarly, becausethe polarity of the primaries P2 and P3 are opposite, the averagevoltage of the capacitor C3 can be equal to the DC power supply Vi.Operations of the power converter 100C when operating in the asymmetricmode are described hereafter.

[t0,t1]

At time t0, the switching elements SW1 and SW2 are turned on underzero-voltage-switching condition and the switching elements SW3 and SW4are remained off. The DC power supply Vi, the inductors L1 and L2, theprimary winding P1, the switching elements SW1 and SW2, and the primarywinding P2 and the inductor L3 form a first loop. The capacitor C2, theswitching elements SW1 and SW2, the primary winding P2, the inductors L3and L5 and the primary winding P4 form a second loop, and the capacitorC3, the switching elements SW1 and SW2, the primary windings P1, theinductors L2 and L1 and the primary winding P3 form a third loop. Theaverage voltages of the capacitors C2 and C3 act as two voltage sources,such that all primary windings P1˜P4 are activated. Hence, themagnetizing currents of the transformer T1 increase linearly and theenergy from the DC power supply Vi is partly delivered to the secondarywinding S1. In addition, the capacitor C1 stores a voltage VC1. At thistime, the voltage stress cross the switching element SW3 is the DC powersupply Vi, and the voltage stress across the switching element SW4 isVi+VC1.

[t1,t2]

At time t1, the switching elements SW1 and SW2 are turned off. Themagnetizing currents discharge the parasitic capacitors of the switchingelements SW3 and SW4. Finally, the parasitic capacitors of the switchingelements SW3 and SW4 are discharged completely and the body diodes ofwhich are turned on.

[t2, t3]

The switching elements SW3 and SW4 are turned on under azero-voltage-switching condition. The DC power supply Vi, the inductorsL1 and L4, the primary winding P3, the switching elements SW3 and SW4,the primary winding P4 and the inductor L5 form a first loop. Thecapacitor C2, the primary winding P1, the inductors L2 and L4 and theprimary winding P3, the switching element SW3, the capacitor C1 and theswitching element SW4 form a second loop. The capacitor C3, theswitching element SW3, the capacitor C1, the switching element SW4, theprimary winding P4, the inductors L3 and L5 and the primary winding P2form a third loop. The voltage −(Vi+VC1) is applied to the primarywindings P1˜P4, such that all primary windings P1˜P4 are activated andthe energy from the DC power supply Vi is partly delivered to thesecondary winding S1. At this time, the voltage stress cross theswitching element SW2 is the DC power supply Vi, and the voltage stressacross the switching element SW1 is Vi+VC1

[t3, t4]

At time t3, the switching elements SW3 and SW4 are turned off. Themagnetizing currents discharge the parasitic capacitors of the switchingelements SW1 and SW2. Finally, the parasitic capacitors of the switchingelements SW1 and SW2 are discharged completely and the body diodes ofwhich are turned on. At time t4, the switching SW1 and SW2 are turned onto resume a new switching cycle.

The power converter 100C can also be operated in a phase shift mode by aphase shift modulation controller. Operations of the power converter100C operated in the phase shift mode are similar to that in theasymmetrical mode, and thus are omitted for briefly.

FIG. 8 shows another embodiment of the power converter according to theinvention. As shown, the power converter 100D is similar to the powerconverter 100C, differing only, in that the node N5B is connected to thenode N6B″ between the capacitor C1 and the switching element SW4 ratherthan the node N6B between the capacitor C1 and the switching elementSW3. Operations of the power converter 100D are similar to those ofpower converter 100C, and thus are omitted for simplification.

FIG. 9 shows another embodiment of the power converter according to theinvention. As shown, the power converter 100E is similar to the powerconverter 100C, differing only, in that the transformer T1 is replacedby two transformers T1 and T2. The primary windings P1 and P4 arebelonged to the transformer T1, and the primary windings P2 and P3 arebelonged to the transformer T2. The transformer T1 further comprises atleast one secondary winding S1 and the transformer T2 further comprisesat least one secondary winding S2. Operations of the power converter100D are similar to those of power converter 100C, and thus are omittedfor simplification.

FIG. 10 shows another embodiment of the power converter according to theinvention. As shown, the power converter 100F is similar to the powerconverter 100C, differing only, in that the node N5B is connected to thenode N6B″ between the capacitor C1 and the switching element SW4 ratherthan the node N6B between the capacitor C1 and the switching elementSW3, and the transformer T1 is replaced by two transformers T1 and T2.The primary windings P1 and P4 are belonged to the transformer T1, andthe primary windings P2 and P3 are belonged to the transformer T2. Thetransformer T1 further comprises at least one secondary winding S1 andthe transformer T2 further comprises at least one secondary winding S2.Operations of the power converter 100F are similar to those of powerconverter 100C, and thus are omitted for simplification.

In addition, the power converters 100A˜100F can also comprises an AC-DCconversion circuit connected to the secondary winding(s), converting theAC output at the secondary winding(s) into the DC voltage(s). FIGS.11A˜11D show the possible rectifier circuits applied to the embodimentsaccording to the invention, but are not limited thereto.

Certain terms are used throughout the description and claims to refer toparticular system components. As one skilled in the art will appreciate,consumer electronic equipment manufacturers may refer to a component bydifferent names. This document does not intend to distinguish betweencomponents that differ in name but not function.

Although the invention has been described in terms of preferredembodiment, it is not limited thereto. Those skilled in the art can makevarious alterations and modifications without departing from the scopeand spirit of the invention. Therefore, the scope of the invention shallbe defined and protected by the following claims and their equivalents.

1. A power converter, comprising: a first series circuit connected inparallel with a direct current (DC) power supply and comprising a firstinductor, a first primary winding, a first switching element and asecond switching element connected in series; a second series circuitconnected in parallel with the DC power supply and comprising a thirdswitching element, a first capacitor, a fourth switching element, asecond primary winding and a second inductor connected in series; and asecond capacitor connected between a first node within the first seriescircuit and a second node within the second series circuit, in which thefirst node is between the first primary winding and the first switchingelement, the second node is between the fourth switching element and thesecond primary winding, and a third node between the first and secondswitching elements is connected to a fourth node within the secondseries circuit.
 2. The power converter as claimed in claim 1, whereinthe first primary winding, the second primary winding and at leastsecondary winding form a transformer.
 3. The power converter as claimedin claim 1, wherein the fourth node is a connection node between thethird switching element and the first capacitor.
 4. The power converteras claimed in claim 1, wherein the fourth node is a connection nodebetween the first capacitor and the fourth switching element.
 5. Thepower converter as claimed in claim 1, wherein the first and secondinductors are parasitic inductors or external inductors.
 6. The powerconverter as claimed in claim 1, further comprising a convertercontroller to control the switching elements in an asymmetrical mode. 7.The power converter as claimed in claim 1, further comprising aconverter controller to control the switching elements in a phase shiftmode.
 8. The power converter as claimed in claim 1, wherein each of theswitching elements comprises one MOSFET, one IGBT, one electromechanicalswitch, one micro-machined switch, or one other active semiconductorswitch with a parallel-connected diode.
 9. A power converter,comprising: a first inductor connected to a direct current (DC) powersupply in series; a first series circuit connected in parallel with theseries-connected DC power supply and first inductor, and comprising asecond inductor, a first primary winding, a first switching element, asecond switching element, a second primary winding and a third inductorconnected in series; a second series circuit connected in parallel withthe series-connected DC power supply and first inductor, and comprisinga fourth inductor, a third primary winding, a third switching element, afirst capacitor, a fourth switching element, a fourth primary windingand a fifth inductor connected in series; a second capacitor connectedbetween a first node within the first series circuit and a second nodewithin the second series circuit, in which the first node is between thefirst primary winding and the first switching element, and the secondnode is between the fourth switching element and the fourth primarywinding; and a third capacitor connected between a third node within thefirst series circuit and a fourth node within the second series circuit,in which the third node is between the second switching element and thesecond primary winding, the fourth node is between the third primarywinding and the third switching element, and a fifth node between thefirst and second switching elements is connected to a sixth node withinthe second series circuit.
 10. The power converter as claimed in claim9, wherein the sixth node is a connection node between the thirdswitching element and the first capacitor.
 11. The power converter asclaimed in claim 9, wherein the sixth node is a connection node betweenthe first capacitor and the fourth switching element.
 12. The powerconverter as claimed in claim 9, wherein the first to the fifthinductors are parasitic inductors or external inductors.
 13. The powerconverter as claimed in claim 9, the first to the fourth primarywindings and at least secondary winding form a transformer.
 14. Thepower converter as claimed in claim 9, the first primary winding, thefourth primary winding and a first secondary winding form a firsttransformer, and the second primary winding, the third primary windingand a second secondary winding form a second transformer.
 15. The powerconverter as claimed in claim 9, further comprising a convertercontroller to control the switching elements in an asymmetrical mode.16. The power converter as claimed in claim 9, further comprising aconverter controller to control the switching elements in a phase shiftmode.
 17. The power converter as claimed in claim 9, wherein each of theswitching elements comprises one MOSFET, one IGBT, one electromechanicalswitch, one micro-machined switch, or one other active semiconductorswitch with a parallel-connected diode